The complex circuitry of the mammalian brain enables the
execution of fundamental cognitive processes such as learning,
speech, and memory. Neural circuits are assembled via specialized
sites of cell-cell contact and communication between neurons
termed synapses. Aberrant synapse development can have pathological
consequences for circuit function as demonstrated by the
manifestation of devastating neurological impairments, including
epilepsy and autism spectrum disorders. The aim of our research
is to define the molecular program that underlies both excitatory
and inhibitory synapse development with the goal of contributing
to a greater understanding of neural circuit formation and
2. mEPSC analysis reveals
defects in the development of functional excitatory
synapses upon RNAi-mediated knockdown of the genes
Rem2, Cadherin-11, Cadherin-13, or Sema4B.
While biochemical and candidate gene approaches have led
to the identification of a large number of molecules that
function at the synapse, the process of synapse development
itself remains poorly understood. Some of the critical questions
in the field include:
- Which proteins are required for excitatory and inhibitory
synapse development and what is their mechanism of action?
- At which specific step in synapse development is the
activity of each protein required?
- How does a neuron maintain the correct balance of
excitatory and inhibitory synapses in order to function
appropriately within a neural circuit?
We have begun to address these important questions using
a novel, forward genetic RNA interference (RNAi)-based screen
in cultured hippocampal neurons (Fig. 1) that has identified
new molecules required for synapse development. Thus far,
we have isolated five new genes that are required for the
proper development of excitatory and/or inhibitory synapses
To investigate the function of the genes isolated in this
and future screens, we utilize a combination of molecular,
biochemical, and electrophysiological approaches in primary
cultures of hippocampal neurons, organotypic hippocampal
slice, acute hippocampal slice, and mouse models. In addition,
as only 30% of genes in the mammalian genome have an ascribed
function, a complete understanding of synapse development
and circuit function depends on identifying the full complement
of molecules that mediate these important processes. Thus,
future screens will focus on isolating molecules that function
to regulate the development of either excitatory or inhibitory
synapses, or that act as general promoters of synaptic development.
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Ghiretti AE and Paradis S (2014). "Molecular mechanisms of activity-dependent changes in dendritic morphology: role of RGK proteins." Trends Neurosci 37(7): 399-407.
Raissi AJ, Scangarello FA, Hulce KR, Pontrello JK, Paradis S (2014). "Enhanced potency of the metalloprotease inhibitor TAPI-2 by multivalent display." Bioorg Med Chem Lett 24(8): 2002-2007.
Ghiretti AE, Kenny K, Marr MT 2nd, Paradis S. (2013). "CaMKII-dependent phosphorylation of the GTPase Rem2 is required to restrict dendritic complexity." J Neurosci 33(15): 6504-6515.
Kuzirian MS, Moore AR, Staudenmaier EK, Friedel RH, Paradis S (2013). "The class 4 semaphorin Sema4D promotes the rapid assembly of GABAergic synapses in rodent hippocampus." J Neurosci 33(21): 8961-8973.
Moore AR, Ghiretti AE, Paradis S (2013). "A loss-of-function analysis reveals that endogenous Rem2 promotes functional glutamatergic synapse formation and restricts dendritic complexity." PLoS One 8(8): e74751.
Raissi AJ, Staudenmaier EK, David S, Hu L, Paradis S (2013). "Sema4D localizes to synapses and regulates GABAergic synapse development as a membrane-bound molecule in the mammalian hippocampus." Mol Cell Neurosci 57: 23-32.
Zeng M, Kuzirian MS, Harper L, Paradis S, Nakayama T, Lau NC (2013). "Organic small hairpin RNAs (OshR): a do-it-yourself platform for transgene-based gene silencing." Methods 63(2): 101-109.
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Paradis S*, Harrar DB*, Lin Y, Koon AC, Hauser
JL, Griffith EC, Zhu L, Brass LF, Chen C, Greenberg
ME (2007) "An RNAi-based Approach Identifies New Molecules
Required for Glutamatergic and GABAergic Synapse Development." Neuron 53: 217-232.
3. An immunocytochemistry
- based assay of inhibitory synapse density demonstrates
that Rem2, Cadherin-11, Cadherin-13, Sema4B or Sema4D
are required for the proper development of inhibitory
Flavell SW, Cowan CW, Kim TK, Greer PL, Lin Y, Paradis S, Griffith EC, Hu LS, Chen C, Greenberg ME (2006). "Activity-dependent regulation of MEF2 transcription factors suppresses excitatory synapse number." Science 311: 1008-1012.
Tolias KF, Bikoff JB, Burette A, Paradis S, Harrar
D, Tavazoie S, Weinberg RJ, Greenberg ME (2005).
"The Rac1-GEF Tiam1 Couples the NMDA Receptor to the Activity-Dependent
Development of Dendritic Arbors and Spines." Neuron 45: 525-538.
Paradis S, Sweeney ST, Davis GW (2001). "Homeostatic
Control of Presynaptic Release is Triggered by Postsynaptic
Membrane Depolarization." Neuron 30: 737-749.
Davis GW, Eaton B, Paradis S (2001). "Synapse Formation
Revisited." Nat. Neurosci. 4: 558-560.
*authors contributed equally
Last edited: June 21, 2016